This invention relates to a liquid supply unit having a pressure supply mechanism that supplies liquid inside of a main tank to a sub-tank incorporated in a liquid droplet jet device. This invention also relates to an inkjet recording apparatus having the liquid supply unit.
Conventionally, various suggestions have been made with regard to liquid supply to a sub-tank for the purpose of supplying liquid to a jet device which ejects liquid droplets onto a recording medium based on image information.
For example, a conventional inkjet recording apparatus with a liquid supply unit is provided with a sub-tank and an ink supply unit. The sub-tank is disposed on a carriage that carries a recording head for scanning. The ink supply unit is disposed separately from the sub-tank. When the ink supply unit becomes in contact with the sub-tank, pressure inside of the sub-tank is decompressed by drawing air inside of the sub-tank with the aid of a suction pump provided in the ink supply unit. As a result, ink is supplied to the sub-tank. The sub-tank is provided with a detection sensor for detecting remaining ink level.
The amount of ink inside of the sub-tank should be preferably maintained at a specific amount at all times. If the amount of ink inside of the sub-tank is small, ink runs out while ink supply to the recording head is performed. Thus, there will be shortage of ink. On the other hand, if the sub-tank is full with ink, the ink might overflow from the sub-tank due to vibration when the inkjet recording apparatus is moved. Surrounding components around the sub-tank might be tainted with ink. In the light of this point, the amount of ink inside of the sub-tank needs to be controlled so as to be maintained consistently at a predetermined amount.
However, the conventional ink supply unit described above is provided with a sensor that detects the amount of ink inside of the sub-tank. Disposition of this kind of sensor requires a space in the interior of the sub-tank for installing the sensor, wiring for the sensor, and a control system for controlling the ink supply unit based on a detection signal. Consequently, the structure of the inkjet recording apparatus becomes complicated. As the number of components increases, not only the cost for the sensor and other components associated with the sensor is needed, but also more steps for installation process are required. Therefore, the manufacturing cost for the inkjet recording apparatus increases.
It would be desirable that, with inexpensive cost and via simple structure, a liquid supply unit can supply liquid to a sub-tank of an inkjet recording apparatus in a manner so that the amount of the liquid in the sub-tank can be maintained at a specific amount.